Shuttle's tiles damaged

Gouge goes through heat shield

NASA weighs spacewalk

HOUSTON -- NASA may have to send astronauts on a special spacewalking mission to mend a 3 1/2 -inch gouge on the shuttle Endeavor's belly that appears to penetrate all the way through two heat shield tiles that protect the orbiter.

Images gathered by lasers and cameras on an extension to the shuttle's robotic arm confirmed yesterday that the divot went through the 1.12-inch thick tile, exposing some of the heat-resistant material below. That material, as well as the tile itself, is designed to protect the orbiter from burning up during re-entry into the Earth's atmosphere.

"It's a fairly deep gouge," said John Shannon, chairman of the mission management team. That team will decide today or tomorrow whether a repair spacewalk is needed.

NASA developed new procedures after foam damaged Columbia's heat shield in 2003, causing the orbiter to disintegrate during re-entry. Shannon said yesterday the agency has the necessary tools and know-how to fix Endeavour's problem.

"This is exactly what we prepared to do," Shannon said. "We are in great shape to go and address this exact problem."

Using data gathered yesterday, engineers will calculate how the divot would react to temperatures reaching 2,300 degrees Fahrenheit on re-entry.

Ice buildup behind a bracket on the external fuel tank popped off a chunk of foam that ricocheted into Endeavour's belly 58 seconds after launch, shuttle managers said. The baseball-size chunk bounced off a strut connecting Endeavour to the tank.

There are three repair options if NASA decides a fix is necessary. An astronaut could paint over the gouge with a black wash that would give some heat protection. Two astronauts could screw a heat-resistant plate over the damaged area. Or an astronaut could use a thick, epoxy-like heat-resistant goo to fill the gap.

The black wash has been tested in the shuttle cargo bay on damaged tiles that were taken to space for that purpose. The other two have been extensively tested on the ground but not in space, Shannon said.

NASA will use computer models of the divot as well as actual heat tiles under simulated re-entry conditions to help them decide whether a repair is needed.

Yesterday's inspection with lasers and a camera targeted four additional areas, all in the vicinity of the main landing gear door under the right wing. Three are smaller divots behind the initial impact, and the other is a less-than-1-inch piece of thermal barrier peeking out of the landing gear door. All were deemed to be acceptable yesterday.

Endeavour astronauts Tracy Caldwell and Barbara Morgan used the shuttle's robotic arm to sweep the laser extension over the area for about three hours.

Managers decided to extend the mission to 14 days from 11 days to allow more work on the International Space Station. That extension will push back Endeavour's landing to Aug. 21.

Today, astronauts Rick Mastracchio and Dafydd (Dave) Williams will make their second spacewalk to replace a faulty gyroscope.